Random musings on the two confusing/controversial FRBR Group 1 entities, which started out as a comment on another forum, but I figure, hey, why not put it here.
Both the “manifestation” and “expression” entities together basically make up the traditional/colloquial idea of ‘edition’. If two different editions have exactly the same (or same enough for contextual purposes) text or content, then they are two manifestations of the same expression. For instance, the 1972 edition and a 1981 edition or whatever. Might have different ISBNs even. But contain the same text, then different manifestations of the same expression.
If, on the other hand, a new edition is seriously revised, then it’s also a new expression, not just a new manifestation.
You can come up with all sorts of grey areas easily, and the FRBR model does not try to precisely instruct you how to decide these grey areas. That’s the role of ‘Guidance’, not ‘model’. The FRBR Model decides it’s useful/necessary to have this distinction, it’s up to implementing communities to specify a useful way to make it as a practical matter. Whether there’s a need for expression AND manifestation, instead of just one ‘edition’ entity is one of the more controversial parts of the FRBR ontology. I think they chose right though.
I also like thinking of this with Elaine Svenonius’ set theory approach, so from the bottom up:
An item, is an actual individual concrete book in your hand.
A manifestation is the set of all items that are identical (or close enough for our purposes) in _physical form_ as well as content.
An expression is the set of all manifestations that are identical in _textual_ or _information_ content. (or close enough for our purposes; an archeologist would consider the coffee stain on the back to be distinguishing information content; we in libraries do not even consider it distinguishing physical form, it’s still part of the same manifestation as the items without coffee stains).
And a work is the set of all expressions that well, consist of the same intellectual work. This is definitely a cultural concept, but it’s one we have and find useful. We consider the audio book version of a book to be the same “book“, just a different version. That’s work.
(If the audio book is abridged it’s a different expression of the work; what if it’s the full text, but read outloud? I’m actually not sure if it should be considered the same or a different expression, it’s kind of arbitrary really, and up to the community to decide.)